The present invention relates to a hydrostatic transmission (hereinafter referred to as HST) that constitutes at least a part of the frame of a vehicle body, and a power transmission arrangement with the HST for vehicle.
Already-known attempts to simplify the arrangement of the vehicle and reduce the cost of the vehicle have involved the use of the housing of the HST also as a part of the frame of the vehicle body, as disclosed in for example Japanese Unexamined Patent Application Publication (Kokai) No. 11-91379.
The HST described in the above-cited Japanese Publication has a hydraulic pump and a hydraulic motor, both of which are mounted on a single block and disposed on the vehicle body via the single block to be aligned parallel to the vehicle width direction. The HST of this arrangement poses the following problems:
If there arises the necessity of increasing the volumes of the hydraulic pump and the hydraulic motor for the vehicle with a high power spec, it will be necessary to mount a block with a large mounting area allowing the large-sized hydraulic pump and hydraulic motor to be aligned parallel to the vehicle width direction on the vehicle body. This may lead to the increase in size of the housing for accommodating such large sized pump and motor, and also the increase in size of the vehicle body itself.
An additional problem inherent to the HSI of the above arrangement lies in the fact that, since the hydraulic pump and the hydraulic motor are to be mounted within the housing together with the block supporting them, these combined members have heavy weight, which may deteriorate the working efficiency. This problem also arises during the hydraulic pump and the hydraulic motor are dismounted from the housing for the maintenance or the like.
As still another problem, the hydraulic pump and the hydraulic motor disposed in one position along the vehicle longitudinal axis may deteriorate the weight balance of the vehicle body.
The present invention has been conceived to solve the above problems. It is an object of the present invention to provide an HST with a housing constituting at least a part of the frame of the vehicle body, which is capable of limiting the increase in size of the frame of the vehicle body, which increase is caused by the increase in size of the hydraulic pump and the hydraulic motor, as well as a power transmission arrangement with the HST for vehicle.
To achieve the above object, there is provided an HST used for vehicle with a vehicle body, which includes a hydraulic pump, a hydraulic motor fluidly connected with the hydraulic pump, a housing accommodating the hydraulic pump and the hydraulic motor, a hydraulic pump block supporting the hydraulic pump and a hydraulic motor block separately arranged from the hydraulic pump block and supporting the hydraulic motor. The housing constitutes at least a part of the vehicle body. The hydraulic pump and the hydraulic motor are disposed along the vehicle longitudinal axis via the hydraulic pump block and the hydraulic motor block.
With the above arrangement, the housing can be manufactured in a reduced size, and hence the vehicle body can have a reduced size. As a result, the vehicle body can be manufactured at low cost. The arrangement with the hydraulic pump and the hydraulic motor respectively supported on the separately arranged blocks can also improve the working efficiency in mounting the hydraulic pump and the hydraulic motor in the housing or dismounting them from the housing. Moreover, unlike the conventional arrangement, it is possible to prevent the hydraulic pump and the hydraulic motor from being concentrated into one position along the vehicle longitudinal axis, resulting in the improved weight balance of the vehicle body.
The hydraulic pump block and the hydraulic motor block may be enclosed by the housing. This arrangement can effectively prevent the blocks from being subjected to the load (bending stress) acting on the vehicle frame. Accordingly, damages against the blocks can be prevented. Moreover, this arrangement can effectively prevent the hydraulic fluid accidentally leaked through hydraulic fluid passages formed in the blocks from flowing to the outside of the housing.
The hydraulic pump and the hydraulic motor may be disposed in sequence from the upstream side to the downstream side of a power transmission path. In this arrangement, the housing has an inner peripheral wall provided with a flange radially inwardly extending from the inner peripheral wall, and the hydraulic pump block is mounted on the flange. The thus arranged flange is formed throughout the circumference of at least a lower side of the inner peripheral wall in the first, housing section. According to this arrangement, it is possible to use as a hydraulic fluid tank a region of the housing on the downstream side of the flange with respect to the power transmission path.
Moreover, the HST may also include a charge pump for replenishing pressurized hydraulic fluid into a hydraulic circuit fluidly connecting the hydraulic pump with the hydraulic motor. In this arrangement, at least one of the hydraulic pump, the hydraulic motor and the charge pump is disposed within a space defined by the hydraulic pump block and the hydraulic motor block within the housing. The thus arranged HST can achieve the effective use of the space within the housing, thereby achieving the reduction in size of, the housing.
According to another aspect of the present invention, there is provided a power transmission arrangement for vehicle with a vehicle body, which includes an HST, a power take-off (PTO) shaft, a PTO power transmission shaft, and a clutch device. The HST in turn includes a hydraulic pump, a hydraulic motor, a housing, a hydraulic pump block, and a hydraulic motor block. The hydraulic pump has a pump shaft extending along the vehicle longitudinal axis and having a first end operatively coupled to a driving power source for enabling the driving power to be inputted to the pump shaft. The hydraulic motor has a motor shaft for non-stepwisely varying the speed of the driving power inputted to the pump shaft in cooperation with the hydraulic pump and then outputting the driving power through the motor shaft. The housing accommodates the hydraulic pump and the hydraulic motor, and designed to constitute at least part of the frame of the vehicle body. The hydraulic pump block and the hydraulic motor block respectively support the hydraulic pump and the hydraulic motor. The hydraulic pump and the hydraulic motor are disposed from the first side to the second side along the vehicle longitudinal axis respectively via the hydraulic pump block and the hydraulic motor block. The PTO shaft is adapted to take off the, driving power of the driving power source and transmit the same to the outside of the vehicle body. The PTO power transmission shaft is disposed on the second side of the pump shaft along the vehicle longitudinal axis and coaxially aligned with the pump shaft, and adapted to transmit the driving power between the pump shaft and the PTO shaft. The clutch device is disposed within a space in the housing defined by the hydraulic pump block and the hydraulic motor block for selectively transmitting the driving power of the pump shaft to the PTO power transmission shaft and shutting off the same.
The power transmission arrangement of the present invention can achieve the reduction in size of the housing, as well as improve the working efficiency in mounting the hydraulic pump and the hydraulic motor in the housing or dismounting them from the housing. Moreover, through the effective use of the space in the housing by disposing the clutch device in the space, it is possible to prevent the housing from being increased in size.
The power transmission arrangement may also include an output shaft disposed coaxially on the second side of the motor shaft along the vehicle longitudinal axis and aligned coaxially with the motor shaft, a counter shaft disposed parallel to the output shaft and operatively coupled to the motor shaft, and a power transmission mechanism for transmitting the driving power from the counter shaft to the output shaft. The counter shaft is a tubular shaft rotatably mounted on the PTO power transmission shaft. According to this arrangement, where the speed change is performed on the downstream side of the HST, it is possible to minimize the distance between the output shaft and the counter shaft, enabling the vehicle body itself to be reduced in size.
The power transmission mechanism may include a plurality of gear transmission devices respectively having different gear ratios. The power transmission mechanism is designed so that one of the plurality of gear transmission devices is selectively brought into engaging state.